Ruthenium(II) carbonyl complexes with phosphine-functionalized PNS type thiosemicarbazone ligands [RuCl(CO)(EPh3)(L)] (1-6) (E = P or As, L = 2-(2-(diphenylphosphino)benzylidene) thiosemicarbazone (PNS-H), 2-(2-(diphenylphosphino)benzylidene)-N-methylthiosemicarbazone (PNS-Me), 2-(2-(diphenylphosphino)benzylidene)-N-phenylthiosemicarbazone (PNS-Ph)) have been synthesized and characterized by elemental analysis and spectroscopy (IR, UV-Vis, (1)H, (13)C, (31)P-NMR) as well as ESI mass spectrometry. The molecular structures of complexes 1, 2 and 6 were identified by means of single-crystal X-ray diffraction analysis. The analysis revealed that all the complexes possess a distorted octahedral geometry with the ligand coordinating in a uni-negative tridentate PNS fashion. All the ruthenium complexes (1-6) were tested as catalyst for N-alkylation of heteroaromatic amines with alcohols. Notably, complex 2 was found to be a very efficient and versatile catalyst towards N-alkylation of a wide range of heterocyclic amines with alcohols. Complex 2 can also catalyze the direct amination of 2-nitropyridine with benzyl alcohol to the corresponding secondary amine. Furthermore, a preliminary examination of performance for N,N-dialkylation of diamine showed promising results, giving good conversion and high selectivity. In addition, N-alkylation of ortho-substituted anilines (-NH2, -OH and -SH) led to the one-pot synthesis of 2-aryl substituted benzimidazoles, benzoxazoles and benzothiazoles, also revealing the catalytic activity of complex 2.
A highly sustainable catalytic protocol
for the coupling of alcohols
and amines for selective monoalkylated amines using Ni(II)–NΛNΛO pincer type complexes through the
borrowing hydrogen methodology is described. An array of Ni(II) catalysts
(1–3) was synthesized and characterized by various
spectral and analytical methods. Furthermore, the distorted square
planar geometry of the complexes (1 and 2) was substantiated with single crystal X-ray diffraction study.
The inexpensive nickel-based catalytic methodology displays a broad
substrate scope for the N-alkylation of aromatic and heteroaromatic
amines using a diverse range of primary alcohols with excellent yields
up to 97%. The present approach is environmentally benign, which liberates
water as the sole byproduct. A short synthesis of drug intermediates
such as mepyramine and chloropyramine illustrates the utility of the
present protocol.
Unsymmetrical and symmetrical azomethines were obtained using the condensation reaction of diamino-thiophene-3,4 dicarboxylic acid diethyl ester with 4-(1-pyrrolidino)benzaldehyde, fluorene-2-carboxaldehyde, 1-methylindole-3carboxaldehyde, and benzothiazole-2-carboxaldehyde. Their thermal, optical, and electrochemical properties were investigated, and the results were supported by calculations using the density functional theory. The studied compounds melted in the range of 170-260°C and can be converted into amorphous materials with high glass transition temperatures between 76 and 135°C. They were thermally stable up to 220-300°C. All imines were electrochemically active and exhibited low energy band gaps below 2 eV (except for one imine with E g = 2.39 eV) determined on the basis of cyclic voltammetry. Most of the azomethines were emissive in solution and in the solid state. Some of them showed both S 1 (first excited state) emission and S 2 (second excited state) emission or only fluorescence from higher excited state, which is first time observed for azomethines. The imine with the most promising properties was tested in a light-emitting diode, and its ability for emission of light under external voltage was demonstrated.
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